Process for producing ammonium sulfate crystals

Abstract

The present invention provides a continuous process for producing ammonium sulfate crystals, wherein said process comprises: i) feeding to a series of crystallization sections, which crystallization sections are heat integrated in series, a solution of ammonium sulfate; ii) crystallizing ammonium sulfate crystals from said solution of ammonium sulfate; iii) purging a fraction of the solution of ammonium sulfate from each of said crystallization sections; and iv) discharging ammonium sulfate crystals from each crystallization section, characterized in that: a fraction of said solution of ammonium sulfate is purged from at least one crystallization section to at least one other crystallization section; and an apparatus suitable for producing ammonium sulfate crystals.

The invention claimed is: 
     
       1. A continuous process for producing ammonium sulfate crystals, wherein the process comprises:
 i) feeding a solution of ammonium sulfate comprising impurities to a heat-integrated series of crystallization sections; 
 ii) crystallizing ammonium sulfate crystals from the solution of ammonium sulfate; 
 iii) purging a fraction of the solution of ammonium sulfate from each of the crystallization sections; and 
 iv) discharging ammonium sulfate crystals from each of the crystallization sections, wherein 
 the ammonium sulfate crystals discharged from each of the crystallization sections are not charged to another crystallization section, and wherein 
 the process further comprises: 
 heat-integrating the crystallization sections by steam, and 
 purging a fraction of the solution of ammonium sulfate from each crystallization section in the series to the next crystallization unit in the series, as defined by descending temperature of steam supply, with the exception that the fraction of the solution of ammonium sulfate purged from the final crystallization section in the series is discharged from the series. 
 
     
     
       2. The process according to  claim 1 , wherein each crystallization section has substantially equal production capacity of ammonium sulfate crystals. 
     
     
       3. The process according to  claim 1 , wherein the series comprises from two to four, crystallization sections. 
     
     
       4. The process according to  claim 1 , wherein each crystallization section comprises an Oslo-type crystallizer. 
     
     
       5. The process according to  claim 1 , wherein the temperature of steam entering the first crystallization section in the series is from 80° C. to 160° C. 
     
     
       6. The process according to  claim 1 , wherein the temperature of steam exiting the last crystallization section in the series is from 40° C. to 60° C. 
     
     
       7. The process according to  claim 1 , wherein each of the crystallization sections has a production capacity which is from 30 kta to 150 kta. 
     
     
       8. The process according to  claim 1 , wherein the ammonium sulfate crystals discharged from the crystallization sections have a mean median diameter which is from 1.0 mm to 4.0 mm. 
     
     
       9. The process according to  claim 1 , wherein the solution of ammonium sulfate is produced from a process for producing ε-caprolactam or acrylonitrile. 
     
     
       10. An apparatus suitable for producing ammonium sulfate crystals according to the process of  claim 1 , comprising:
 i) a series of crystallization sections of substantially equal production capacity of ammonium sulfate crystals which are configured to be heat integrated with respect to steam; 
 ii) a steam supply system integrating the crystallization sections in series; 
 iii) a feed of ammonium sulfate solution; and 
 iv) a system of removal of ammonium sulfate crystals; wherein 
 the ammonium sulfate crystals discharged from each of the crystallization sections are not charged to another crystallization section, and wherein 
 each crystallization section is connected by a purge line to the next crystallization section in the series, as defined by descending temperature of steam supply, with the exception that a purge from the final crystallization section is discharged from the series. 
 
     
     
       11. The apparatus according to  claim 10 , wherein each crystallization section comprises an evaporative crystallizer and solid-liquid separation equipment. 
     
     
       12. The apparatus according to  claim 10 , wherein each of the crystallization sections is sized so as to have a production capacity from 30 kta to 150 kta.